From f35fe407b39b07927e8198f666fade408fd3aa41 Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Fri, 11 Oct 2019 14:09:53 +0200
Subject: [PATCH] text: tighten clip bounds for Editor and Label

We're about to remove the extra padding from Editor. To do that, the
clipping must account for text drawing that lie outside the viewport.

With accurate clip bounds, use it for Label as well.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 text/editor.go | 15 ++++++++-------
 text/label.go  | 34 +++++++++++++++++++---------------
 2 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/text/editor.go b/text/editor.go
index 26dd18d1..e4a42924 100644
--- a/text/editor.go
+++ b/text/editor.go
@@ -266,9 +266,7 @@ func (e *Editor) draw(gtx *layout.Context, s *Shaper, font Font) {
 		X: -e.scrollOff.X + e.padLeft,
 		Y: -e.scrollOff.Y + e.padTop,
 	}
-	clip := image.Rectangle{
-		Max: image.Point{X: e.viewSize.X, Y: e.viewSize.Y},
-	}
+	clip := e.clipRect()
 	it := lineIterator{
 		Lines:     e.lines,
 		Clip:      clip,
@@ -297,9 +295,6 @@ func (e *Editor) drawCaret(gtx *layout.Context) {
 	}
 	carLine, _, carX, carY := e.layoutCaret()
 
-	clip := image.Rectangle{
-		Max: e.viewSize,
-	}
 	var stack op.StackOp
 	stack.Push(gtx.Ops)
 	carX -= e.carWidth / 2
@@ -312,7 +307,7 @@ func (e *Editor) drawCaret(gtx *layout.Context) {
 		X: -e.scrollOff.X + e.padLeft,
 		Y: -e.scrollOff.Y + e.padTop,
 	})
-	carRect = clip.Intersect(carRect)
+	carRect = e.clipRect().Intersect(carRect)
 	if !carRect.Empty() {
 		paint.PaintOp{Rect: toRectF(carRect)}.Add(gtx.Ops)
 	}
@@ -336,6 +331,12 @@ func (e *Editor) SetText(s string) {
 	e.prepend(s)
 }
 
+func (e *Editor) clipRect() image.Rectangle {
+	clip := textPadding(e.lines)
+	clip.Max = clip.Max.Add(e.viewSize)
+	return clip
+}
+
 func (e *Editor) scrollBounds() image.Rectangle {
 	var b image.Rectangle
 	if e.SingleLine {
diff --git a/text/label.go b/text/label.go
index 9ba40209..ce4e4fc7 100644
--- a/text/label.go
+++ b/text/label.go
@@ -98,11 +98,8 @@ func (l Label) Layout(gtx *layout.Context, s *Shaper) {
 	}
 	dims := linesDimens(lines)
 	dims.Size = cs.Constrain(dims.Size)
-	padTop, padBottom := textPadding(lines)
-	clip := image.Rectangle{
-		Min: image.Point{X: -inf, Y: -padTop},
-		Max: image.Point{X: inf, Y: dims.Size.Y + padBottom},
-	}
+	clip := textPadding(lines)
+	clip.Max = clip.Max.Add(dims.Size)
 	it := lineIterator{
 		Lines:     lines,
 		Clip:      clip,
@@ -135,16 +132,23 @@ func toRectF(r image.Rectangle) f32.Rectangle {
 	}
 }
 
-func textPadding(lines []Line) (padTop int, padBottom int) {
-	if len(lines) > 0 {
-		first := lines[0]
-		if d := -first.Bounds.Min.Y - first.Ascent; d > 0 {
-			padTop = d.Ceil()
-		}
-		last := lines[len(lines)-1]
-		if d := last.Bounds.Max.Y - last.Descent; d > 0 {
-			padBottom = d.Ceil()
-		}
+func textPadding(lines []Line) (padding image.Rectangle) {
+	if len(lines) == 0 {
+		return
+	}
+	first := lines[0]
+	if d := first.Ascent + first.Bounds.Min.Y; d < 0 {
+		padding.Min.Y = d.Ceil()
+	}
+	last := lines[len(lines)-1]
+	if d := last.Bounds.Max.Y - last.Descent; d > 0 {
+		padding.Max.Y = d.Ceil()
+	}
+	if d := first.Bounds.Min.X; d < 0 {
+		padding.Min.X = d.Ceil()
+	}
+	if d := first.Bounds.Max.X - first.Width; d > 0 {
+		padding.Max.X = d.Ceil()
 	}
 	return
 }